Engine driven vehicles are known, which drive a generator by an engine when driving is stopped to supply power to an external load. Such a vehicle is disclosed, for example, in Japanese Patent Laid-Open No. 2001-231106.
In recent years, in engine driven vehicles such as ATVs (All Terrain Vehicles, so-called buggies), tractors, or recreation vehicles that are designed for driving on rough ground, a commercial AC output of AC 100 V or AC 200 V (50 Hz or 60 Hz) has been supplied from a power supply unit that uses a generator driven by an engine as a power supply to an external load in a separate system from electrical components of the vehicle such as an ignition device, a fuel injection device, a head light, or a direction indicator, when the vehicle is stopped.
As a generator to be a power supply of the power supply unit, a generator provided separately from a generator that drives electrical components of a vehicle is sometimes used, or a generator that drives electrical components of a vehicle is sometimes shared.
A power supply unit incorporated in such a vehicle has a construction suitable for a generator mounted to an engine. For example, when a magneto AC generator that cannot perform field control is used as a generator mounted to the engine, a power supply unit is comprised of a rectifier that rectifies an output of the generator, an inverter that converts an output of the rectifier into an AC output at a commercial frequency, and a filter that removes harmonic components from the output of the inverter.
When a synchronous generator that can perform field control is used as a generator mounted to the engine, a power supply unit is comprised of the generator, and a circuit that controls a field of the generator.
A control device for the engine driven vehicle incorporating such a power supply unit includes: engine control means (ECU) that performs various controls required for operating the engine when the vehicle is driven and the generator is driven; a mode selection switch for selecting a control mode between a control mode for driving vehicle and a control mode for generating electric power; and generation control means for arithmetically operating a target rotational speed of the engine required for supplying predetermined power from the power supply unit to a load, or for controlling a circuit such as an inverter provided in the power supply unit, when the mode selection switch selects the control mode for generating electric power.
The engine control device is comprised so as to perform control of an ignition timing and a fuel injection amount (when an injector is used as fuel supply means) of the engine, idling control for stabilizing idling of the engine, control for matching a rotational speed of the engine with the target rotational speed provided from the generation control means when the control mode for generating electric power is selected, control for limiting the rotational speed to a limit rotational speed or lower in order to prevent damage to the engine, in accordance with control conditions such as the rotational speed of the engine, a throttle valve opening degree, an engine temperature, a gear position of a transmission provided between the engine and wheels, or the like. Generally, the limit rotational speed of the engine is set equal to a mechanical limit speed of the engine.
In the vehicle having the generator for driving the external load as described above, if a gear position of a power transmission device provided between a crankshaft of the engine and driving wheels is in a position for transmitting power (a position other than a neutral position or a parking position) in error when the generator is driven, an increase in the rotational speed of the engine for driving the generator may cause runaway of the vehicle.
Thus, the generation control means is comprised so as to control to rotate the engine at a desired rotational speed only when the mode selection switch selects the control mode for generating electric power, and a gear position sensor detects that the gear position of the power transmission device is in an N (neutral) position or a P (parking) position.
Japanese Patent Laid-Open No. 2001-231106 describes that a rotational speed is controlled by generation control means only when a gear position sensor detects that a gear position of a power transmission device is in a position for cutting power transmission.
The generation control means has a construction suitable for a construction of a generator. For example, when a magneto AC generator is used as a generator, the generation control means is comprised of target rotational speed arithmetic operation means for arithmetically operating a target rotational speed of the engine required for generating a predetermined output from the inverter, and inverter control means for controlling the inverter so as to output an AC voltage at a predetermined frequency from the inverter.
The target rotational speed arithmetically operated by the generation control means is provided to the engine control means. The engine control means controls an output control device of the engine so that a deviation becomes zero between the current rotational speed of the engine and the target rotational speed provided from the generation control means, and controls the engine to keep the rotational speed at the target rotational speed.
When a synchronous generator that can perform field control constitutes the power supply unit, a main unit of the generation control means is comprised of means for providing a target rotational speed (a fixed value) of the engine required for keeping an output frequency of the synchronous generator at a predetermined commercial frequency to the engine control means, and field current control means for controlling a field current of the generator so as to keep an output voltage of the synchronous generator within a set range.
The engine control means is comprised of an electronic control unit (ECU) including a microprocessor, an ignition device, an injector drive circuit, or the like.
The generation control means is constructed using the microprocessor of the ECU or a microprocessor dedicated for the generation control means.
The output control device of the engine is a device operated for adjusting the rotational speed of the engine, and a valve that is operated by an actuator to adjust an intake air amount of the engine is used as the device. As the valve that adjusts the intake air amount of the engine, an electronically controlled throttle valve, as well as an ISC valve (Idle Speed Control Valve) or an IAC valve (Idle Air Control valve) that adjusts the amount of bypassing air passing so as to bypass the throttle valve may be used.
As described above, the ECU provided in the engine control device controls to limit the rotational speed of the engine to the limit rotational speed or lower. In the conventional control device, the limit rotational speed of the engine is equally set in the driving time control mode and in the control mode for generating electric power, and therefore, operating an axle allows the rotational speed of the engine to increase to a high limit rotational speed in the driving time control mode even in the control mode for generating electric power.
In the driving time control mode, providing a switch between an output terminal of the generator and a circuit closer to a load than the output terminal of the generator and opening the switch, or the like may prevent problems that an excessive voltage is applied to the circuit closer to the load than the generator (for example, a rectifier or an inverter) to damage circuit components, when the rotational speed of the engine increases to increase the output voltage of the generator.
However, in the control mode for generating electric power, the output voltage of the generator is necessarily in a state of application to the circuit closer to the load, and therefore an excessive increase in the rotational speed of the engine may cause damage to electronic components of the circuit closer to the load.
When the engine is controlled in the control mode for generating electric power, the engine output control device is generally controlled so that the generation control means keeps the rotational speed of the engine at the target rotational speed, which prevents an excessive increase in the rotational speed of the engine to cause disadvantages as described above. However, when a driver operates an axle in error to open the throttle valve during generation, or when an abnormality occurs in the engine output control device, the rotational speed of the engine may increase to exceed the target rotational speed. In this case, the ECU accepts the increase in the rotational speed of the engine up to the limit rotational speed set to an upper limit value of the rotational speed of the engine accepted while vehicle driving, which may cause damage to the components of the circuit closer to the load than the generator.